Glow-discharge lamp tuning indicator



Afig, 23, 1949. Q 0. c. PINKERTON 2,479,954

GLOW-DISCHARGE LAMP TUNING INDICATOR Filed Sept. 11, 1947 Fig. la.

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RE oN ANCE FREQUENCY V Inventor-z David CUFinkerton,

His Attorney Patented Aug. 23, 1949 GLOW-DISCHARGE, LAMP TUNING INDICATOR David C. Pinkerton, Syracuse, N. Y, assign'or t6" General Electric Com New York pany, a corporationof- Application September 11,1947 serial Naif 3 ,391 3 Claims. (cmsoqt) My invention relates to tuning indicators, and more particularly to glow-discharge lamp indicators as may be used to facilitate proper tuning of rad o transmitters.

In the engineering design of a radio transmitter, it is desirable to provide a compact, eflicient method of indicating proper operation and precise tuning. In the prior art, it has been customary to connect one electrode of a neon lamp or similar gas-discharge device to the antenna circuit While allowing the other electrode to float free (i. e., remain unconnected). In this manner, the gas-discharge device is made to give a general indication of the tuning of the antenna output, a glow discharge being" maintained when the output circuit is tuned to resonance.

This method of tuning indication has certain inherent disadvantages. Firstly, the indication of the tuning peak is very broad since the lamp frequently will not glow until a relatively high potential is applied, at which time breakdown occurs and conduction is abruptly initiated. Furthermore, the lamp is operated in the range of essentially constant discharge current; hence, the

brilliance and the characteristic shape of the.

glow do not materially change throughout the tuning range. Secondly, the operation of a tuning indicator at high potential absorbs considerable radio frequency power from the antenna circuit, thus rendering such an indicator impractical for low power transmitters. I

It is a primary object of my invention to provide an improved tuning indicator comprising a glow-discharge device for indicating conditions of resonance in an oscillatory circuit.

It is a particular object of my invention to provide compact and eficient means for precise tuning indication of a radio transmitter.

Another object of my invention is to provide an accurate tuning indicator, comprising a gasfilled glow-discharge lamp, which is particularly adapted for use in a low power radio transmitter or radio frequency amplifier.

features of my invention which I believe to be novel are set forth with particularity inthe appended claims. My invention itself, however, with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 is a" schematic diagram of a circuit which embodies invention; Fig. 1a is a modification of that m n of the circuit of Fig. 1 lying within the dasl d rectangle; Fig. 2 is a partial section of a giow-discharge lamp which may be used as the indicator devic'e in the circuit'of Fig. 1 and Fig. 3 is aselec'tivity characteristic curve for the in- ClICat'OIi of the circuitoi Fig; 1. Like reference numerals indicate like elements in the several figures.

R'eferringjto Fig. 1 of the accompanying drawing,.there is shown in schematic form a circuit which may'comprise the'poweram'plifier stage of aradio transmitter". An electron discharge device l isshow'n comprising cathode, control grid, and anode electrodes 2, 3, 4, respectively. Positive direct energizing voltage +B is applied to the anode" {of the device-l through a parallel circuit 5 comprising @0611 or inductance 6 and a variable condenser or capacitance l. The customary alternating current by-pass condenser 8 is supplied across't'he source of direct energizing voltage. The circuits for the cathode 2 and control grid 3 of device I' are omitted for the sake of simplifying the drawing since the details or these circuits have no bearing on my invention.

The coil 6 is provided with a tap 9 near the low radio frequency potential end. To the tap 9 is attachedone electrode l0 of a gas-discharge device ll, 7 The other electrode 12 of the device II is connected to ground through a high resistance l3 which may, for example,be of the order of 5 to 20 megohms.

The radio frequency voltage developed across the parallel circuit 5 is inductively coupled to a suitable load (not shown) which may be an antenna, for example, by means of a coupling coil l4 and a coaxialline t5.

Fig. la shows an' alternative arrangement, the circuit beingidentical with that of Fig. 1 except for the portion-within the dashed rectangle. In this modification; the parallel circuit 5 is tuned by means-of avariable inductance and the output of the power amplifier is direct-coupled to the antenna or other radio frequency load by means of a capacitor Hi.-

In operation, the output voltage is very small at all frequencies except the carrier frequency. For maximum output voltage, the parallel circuit 5 is tuned to resonance by means of the variable condenser 1-, such-resonance occurring at a frequency equal to the carrier frequency.

In particular, my tuning indicator operates as follows: The series combination of the device II and the resistor 1-3 is connected across a small portion I l ofthe inductance 5; Assume that the parallel circuit 5 is not tuned to resonance. There exists across the portion l! a small direct voltage such as a neon glow-discharge tube.

characteristic colors obtain with the use of other inert gases, such as grypton, xenon, etc, in the device H. a

Now, as the parallel circuit 5 is tuned toward resonance, an increasing radio frequency potential is developed across the inductance 6, and in turn, a smaller increasing radio frequency potential is developed across the tapped portion l1. As the radio frequency voltage across the tapped portion 11 increases, the characteristic glow discharge becomes more brilliant, until at resonance a maximum brilliancy is attained. As the parallel circuit 5 is detuned away from resonance, the brilliancy decreases. If the'carrier frequency, or resonant frequency of the parallel circuit 5,

is in the very high frequency range (e. g., 100

megacycles per second), and ifthe device H is a neon lamp, the color of the glow discharge also changes gradually from the dull orange characteristic of direct discharge current to the violetblue or blue characteristic of the higher frequencies, thus giving an additional indication of proper tuning. For other inert gases, the discharge progresses through different characteristic color cycles.

Fig. 2 shows in cross section a neon lamp which may be used as the device I l of Fig. 1. A pressuresealed envelope I8 is evacuated and filled with an inert gas such as neon. Two elongated rodshaped electrodes l0, l2 are provided, electrode being conductively connected to the terminal I9, and electrode l2 being conductively connected to the base 20. Suitable means are provided for mounting the lamp II in a socket (not shown). Further constructional details of the lamp H are believed unnecessary as such details are well known in the art.

The use of a lamp with spaced, elongated electrodes, such as that shown in Fig. 2, provides a further indication of precise tuning. In addition to the aforementioned brilliancy and color effects, the length of the glow discharge increases to a maximum as the parallel circuit (Fig. l) is tuned toward and through resonance.

Fig. 3 shows, in graphical form, the indicating action of the device ll (Fig. 1). The brilliancy (or length) of the glow discharge is shown as a function of frequency. At zero frequency, the only discharge present is the characteristic glow due to the direct bias voltage. As the parallel circuit 5 (Fig. 1) is tuned toward and through resonance, the frequency increases, and the brilliancy and length of the glow discharge attain a maximum at resonance. I have found that the peak of the curve of Fig. 3 may be made very sharp by properly adjusting the tap 9 (Fig. 1) on the inductance 6 and by selecting a lamp of proper construction and voltage rating.

In summary, my invention provides very selective means for indicating precise tuning of a high frequency circuit, such as a radio frequency amplifier in a radio transmitter. Since the indicator lamp utilizes a very small portion of the output "of the power amplifier, little output power is sacrificed; therefore, my invention is particularly adapted to tuning indication for low power transmitters.

While I have shown particular embodiments of my invention for purposes of illustration, it will be understood that manymodifications and variations, both in circuit arrangement and lamp construction, may be made, and I contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A tuning indicator system comprising a first circuit including an inductance and a capacitance and adapted to be tuned to resonance at a given frequency, a second circuit comprising a glowdischarge device and a tapped portion of said inductance, means for developing an oscillatory voltage across said first circuit having a maximum vaiue at said frequency, thereby to excite said discharge device to produce a characteristic oscillatory glow discharge, and means to sensitize said device comprising means to maintain a relatively low value of direct current continuously through said device.

2. A tuning indicator system comprising a radio frequency amplifier having an anode circuit, said anode circuit comprising a parallel inductancecapacitance circuit adapted to be tuned to resonance at a given frequency in series with a source of direct anode operating current, and a resonance indicating circuit comprising a gas-filled glow-discharge device connected between a point on said source and a point on said inductance, said points being adjusted to maintain a low value of direct current at all times through said device and to provide a gradual increase in' radio frequency discharge current through said device up to a maximum as said anode circuit is tuned toward and through resonance.

3. A tuning indicator system comprising a radio frequency amplifier having an anode circuit, said anode circuit comprising a parallel inductance capacitance circuit adapted to be tuned to resonance at a given frequency in series with a source of direct anode operating voltage, and a resonance indicating circuit comprising a resistor in series with a gas-filled glow-discharge device having a pair of spaced elongated electrodes, said indicating circuit being energized with a relatively low value of. direct current from said source just sufficient to maintain said glow-discharge device continuously conductive and also energized with radio frequency current supplied from a tapped point on said inductance, said point being adjusted so that a characteristic radio frequency glow discharge develops and expands along said electrodes to a well-defined maximum length and brilliance as said anode circuit is tuned toward and through resonance.

DAVID C. PINKERTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,180,075 Pichon Apr. 18, 1916 2,128,395 Berndt et al 1- Aug. 30, 1938 2,358,352 Sherwood Sept. 19, 1944 

